This invention relates to a rotation-support apparatus, and more particularly to a rotation-support apparatus that is used, for example, for supporting planetary gears that are installed in a planetary-gear mechanism of an automatic transmission for an automobile so that they freely rotate around the planetary shafts that are located in a carrier. Moreover, the rotation-support apparatus of this invention is particularly constructed with a retainer so that high-speed rotation is possible, and its construction makes it possible to adequately maintain the durability of the retainer.
Of the rotation-support units for an automobile transmission or various mechanical apparatuses, radial-needle bearings are installed in the portions where large radial loads are applied. For example, a known planetary-gear-type transmission of an automatic transmission for an automobile as described in patent document 1 supports planetary gears by way of radial-needle bearings so that they rotate freely with respect to a carrier. FIG. 9 shows an example of this kind of a rotation-support apparatus for planetary gear that supports a planetary gear so that it rotates freely with respect to the carrier. In the case of the construction shown in FIG. 9, both end sections of planetary shafts 3 are supported by and attached to a plurality of locations around the circumferential direction of a pair of parallel support plates 2a, 2b of the carrier 1. Also, a planetary gear 4 is supported by a radial-needle bearing 5 around the middle section of the planetary shaft 3 so that rotates freely.
This radial-needle bearing 5 holds a plurality of needles 6 by way of a retainer 7 so that they can roll freely, and with the outer peripheral surface around the middle section of the planetary shaft 3 as a cylindrical-shaped inner ring raceway 8, and the inner peripheral surface around the inside of the planetary gear 4 as a cylindrical-shaped outer ring raceway 9, the rolling surfaces of the respective needles 6 come in rolling contact with the inner ring raceway 8 and outer ring raceway 9. Also, floating washers 10a, 10b are placed between the both end surfaces in the axial direction of the planetary gear 4 and the inside surfaces of the support plates 2a, 2b, respectively, which makes it possible to reduce the friction force that acts between both end surfaces in the axial direction of the planetary gear 4 and the inside surfaces of the support plates 2a, 2b. As disclosed in patent document 1, a typical prior needle bearing that supports a planetary gear that is installed in a planetary-gear mechanism of an automatic transmission for an automobile is a full complement needle-type bearing that does not have a retainer. On the other hand, recently, in order to make it possible for the planetary gear to rotate at high speed, and in order to avoid contact between adjacent needles in the circumferential direction, use of a radial-needle bearing having a retainer 7 as disclosed in patent document 2, for example, is increasing.
As shown in detail in FIGS. 10 and 11, the retainer 7 of the aforementioned radial-needle bearing 5 comprises: a pair of ring-shaped rim sections 11 that are arranged so that they are separated from each other by an interval in the axial direction (left-right direction in FIGS. 9 and 11), and plurality of column sections 12. The column sections 12 are arranged intermittently around in the circumferential direction, and both end sections of each column section 12 are continuous with the outer-radial portion of the opposing inside surfaces of the rim sections 11. Moreover, the middle section in the axial direction of each of the column sections 12 has a trapezoidal bent shape that bends inward in the radial direction.
In other words, these column sections 12 comprise: a pair of straight sections 13 on the outer-radial side, a pair of inclined sections 14 and a straight section 15 on the inner-radial side. Of these, both straight sections 13 on the outer-radial side are such that the base-end sections are continuous with the outer-radial section on the inside surface of both rim sections 11, and they are parallel with the center axis of the retainer 7. Moreover, the inclined section 14 are such that the base-end sections are continuous with both straight sections 13 on the outer-radial side, and they incline inward in the radial direction of the retainer 7 going toward the middle section in the axial direction of the retainer 7. Furthermore, the straight section 15 on the inner-radial side is such that both ends are continuous with the tip-end sections of both inclined sections 14, and is parallel with the center axis of the retainer 7.
Also, the spaces that are surrounded by both side surfaces in the circumferential direction of column sections 12 that are adjacent in the circumferential direction, and the opposing inside surfaces of both rim sections 11 form pockets 16, and the needles 6 are held in these pockets 16 so that they can roll freely. The retainer 7 has stopper protrusions 17 located at locations on the side surfaces of both ends of the column sections 12 so that they align with each other and they are adjacent to each other in the circumferential direction. These stopper protrusions 17 are for preventing the needles 6 that are held inside the pockets 16 so that they can roll freely from coming out of the pockets 16 in the outward radial direction. In other words, when the needles 6 are installed together with the retainer 7 between the inner ring raceway 8 and outer ring raceway 9 (see FIG. 9), these needles 6 must be held in the pockets 16 in a state in which they are prevented from coming out in the radial direction.
Therefore, the stopper protrusions 17 are located on the opening of the pockets 16 further outward in the radial direction than the pitch circle of the needles 6 so that they face each other, and the space D17 (see FIG. 10) between the edges of a pair of tip ends of these stopper protrusions 17 is less than the outer diameter D6 (see FIG. 9) of the needles 6 (D6>D17). Also, of the surfaces on both sides in the circumferential direction of the straight sections 15 on the inner-radial side of the middle section of the column sections 12, the edge of the inner end in the radial direction of the retainer 7 is located further inward in the radial direction than the pitch circle of the needles 6, and the space D15 (see FIG. 10) between the edges of a pair of inner ends is also less than the outer diameter D6 of the needles 6 (D6>D15).
In order to hold the needles 6 in the pockets 16, these needles 6 are inserted into the pockets 16 from the inner-radial side of the retainer 7. When doing this, the needles 6 elastically widen the spaces D15 between the edges of the pairs of inner ends of the straight sections 15 on the inner-radial side, and these needles 6 pass between the edges of these pairs of inner ends. With the needles 6 held in the pockets 16 in this way, the stopper protrusions 17 prevent the needles 6 from coming out in the outward radial direction, and similarly the side surfaces of the straight sections 15 on the inner-radial side of the column sections 12 prevent the needles 6 from coming out in the inward radial direction.
In the case of the prior radial-needle bearing 5 described above, when the needles 6 inside the pockets 16 formed in the retainer 7 move in the circumferential direction of the retainer 7, the rolling surfaces of the needles 6 come in direct contact with the side surfaces in the circumferential direction of the straight sections 15 on the inner-radial side of the column sections 12. In the case of a retainer 7 that is installed in a radial-needle bearing 5 for supporting a planetary gear 4 around the planetary shaft 3 of a planetary-gear mechanism, the rolling surfaces of the needles 6 do not come in direct contact with just one of the side surfaces in the circumferential direction of the straight sections 15 on the inner-radial side, but come in direct contact with alternate side surfaces in the circumferential direction due to the revolving movement of the needles 6. As a result, a moment load is applied to the column sections 12 alternately in different directions, which makes it difficult to maintain the durability of the continuous sections between both end sections of the columns sections 12 and the rim sections 11.
The reason for this will be explained with reference to FIG. 12. A planetary gear 4 that is installed in a planetary-gear mechanism revolves around a sun gear (not shown in the figure) as the carrier 1 rotates, and due to the engagement between this sun gear and a ring gear (not shown in the figure), the planetary gear 4 rotates around the planetary shaft 3. Also, the needles 6 of a radial-needle bearing 5 that supports the planetary gear 4 so that it rotates freely around the planetary shaft 3 revolve while rotating around the planetary shaft 3 due to the rotation of the planetary gear 4. In this case, the needles 6 receive a centrifugal force due to the revolving movement around the sun gear, which causes the needles 6 to move outward in the radial direction of the carrier 1 and the needles 6 are pushed against the side surface in the circumferential direction of the column sections 12.
For example, the case in which the planetary shaft 3 revolves together with the carrier 1 in the direction of the arrow α in FIG. 12 around the sun gear, and the planetary gear 4 rotates in the direction of arrow β in the same figure, will be considered. In this case, centrifugal force due to the revolving movement in the direction of the arrow α applies a force on the needles 6 as shown by the arrow γ in the same figure in the direction toward the outer-radial direction of the carrier 1. Also, due to this force in the direction of this arrow γ, the needles 6 are pushed against the side surfaces in the circumferential direction of the column sections 12. The size of the force that pushes the needles 6 against the side surfaces in the circumferential direction of the column sections 12 in this way, differs depending on the position of the needles 6 with respect to the planetary shaft 3, and needles 6 that are located in the orthogonal directions with respect to the radial direction of the carrier 1 from the center of the planetary shaft 3 (left and right end sections in FIG. 12), are pushed the strongest against the side surfaces of the column sections 12. Moreover, when seen from these column sections 12, each time the retainer rotates one time, the needles 6 are alternately pushed with a strong force in the opposite direction. As a result, force is alternately applied in the circumferential direction to the column sections 12, and the continuous sections between the column sections 12 and both rim sections 11 fatigue easily, making it difficult to maintain durability of the retainer 7.
As construction that regulates the position in the radial direction of the retainer 7 that is installed in the radial-needle bearing 5, there is a so-called needle guide, so-called outer ring guide and so-called inner ring guide. Of these, the needle guide regulates the position in the radial direction of the retainer 7 by engagement between the pockets 16 of the retainer 7 and the rolling surfaces of the needles 6. Moreover, the outer ring guide regulates the position in the radial direction of the retainer 7 by bringing the outer peripheral surface of the retainer 7 close to the outer ring raceway 9. Furthermore, the inner ring guide regulates the position in the radial direction of the retainer 7 by bringing the inner peripheral surface of the retainer 7 close to the inner ring raceway 8. In the case of any of the aforementioned construction for regulating the position in the radial direction of the retainer 7, the needles 6 are alternately pushed against both side surfaces in the circumferential direction of the column sections 12 due to centrifugal force caused by rotation of the carrier 1, so the continuous sections between the column sections 12 and both rim sections 11 fatigue easily.
However, by adopting the aforementioned outer ring guide or inner ring guide and moving all of the column sections 12 to the outer-radial side or inner-radial side of the pitch circle of the needles 6, a partial force in the radial direction occurs in the force that the needles 6 push the column sections 12. As a result, it is thought to be possible to alleviate a little of the stress in the continuous sections between the column sections 12 and both rim sections 11 that cause fatigue. However, before installing the needles 6 held in the pockets 16 between the outer ring raceway 9 and inner ring raceway 8, it is necessary to have separate construction (construction separate from that shown in FIGS. 9 to 11) for preventing the needles 6 from coming out of the pockets 16. Of the aforementioned outer ring guide and inner ring guide, the outer ring guide makes it possible to increase the area where the guide surfaces are opposed, which from the aspect of being able to reduce the surface pressure of that portion is superior than that of the inner ring guide.    Patent Document 1    Japanese Utility Model Application Publication No. H5-62729    Patent Document 2    Japanese Patent Application Publication No. H8-270658